#!/usr/bin/perl
use strict;
use warnings;

if (@ARGV != 3)
{
  die "usage: $0 start end ttyrec\n";
}

my $frame = 0;
my $DEC   = 0;
my $start = shift || 1;
my $end   = shift || -1;
my $prev  = '';
my $handle;

open($handle, '<', $ARGV[0]) or die "Unable to open '$ARGV[0]': $!";

while ((my $hgot = read($handle, my $hdr, 12)) > 0)
{
  ++$frame;

  die "Unexpected EOF in '$ARGV[0]' frame $frame header (expected 12 bytes, got $hgot)" if $hgot < 12;

  my @hval = unpack "VVV", $hdr;
  my $dlen = $hval[2];
  my $dgot = read $handle, my ($data), $dlen;

  die "Unexpected EOF in '$ARGV[0]' frame $frame data (expected $dlen bytes, got $dgot)" if $dgot < $dlen;

  $DEC = 1 if $data =~ /\e\)0/;

  if ($frame < $start)
  {
    # we can modify $data because we're not printing it anyway
    $prev = '' if $data =~ s/.*\e\[2J//;
    $prev .= $data;
  }

  if ($frame == $start && $frame > 1)
  {
    $data = "\e\[2J" . $prev . $data;
    $data = "\e)0"   . $data if $DEC;
  }

  $hval[2] = length($data);
  $hdr = pack "VVV", @hval;

  print "$hdr$data" if $frame >= $start && ($end == -1 || $frame <= $end);
}